Well for a start i'd seperate the fish!
If you don't seperate the male and female beta fish the male one will more than likely become very aggresive towards the females. There's also a good chance he'll turn aggressive towards your shark, seeing it as a rival.
I'd also be wary about keeping Beta's with platys, as though several sites state they can be kept together, I found that these usually end up as fish food for betas too.
As for feeding, I tend to feed mine a small pinch every couple of days.